Surface movement above old coal longwalls after mine closure

Although most subsidence occurs in the months and years after mining by the longwall method, surface movement is still occurring many decades after the mining. The aim of the study is to quantify the long term behavior. Satellite data (radar-interferometry) were analyzed to study an area of about 2 km2 during the 18 years following the closure of the underground infrastructure and the flooding of the underground workings and rock mass. It was observed that, on average, a residual downward movement took place till 7-12 years after the closure, followed by a clear uplift. However, the first signs of an uplift occurred in certain sub-areas 3-4 years after the closure. Zones within the area studied were identified with either larger or smaller movements. However, the spatial variation of the surface subsidence or uplift could not be directly explained by the characteristics of mining.